The proposed study is aimed at investigating the transport and deposition of hygroscopic aerosols in Plexiglas models of the human respiratory tract under humid conditions and in the lungs of anesthetized dogs. In the study with Plexiglas models, various types of hygroscopic particles such as droplets of NaCl solutions will be used as test aerosols, and simulated respiratory flows will be provided by a mechanical breathing machine. Variables to be studied include air flow rate, particle size, and chemical composition of the particles. The results will be compared with the deposition data of non-hygroscopic aerosols. In the study with anesthetized dogs, the regional distribution of the deposited particles in the lungs will be studied using hygroscopic aerosols generated from radiopague substances such as Hydropague Megluline. The animal study is aimed at investigating the effects of breathing pattern, particle size, and chemical composition of the particles on regional deposition. The data obtained from Plexiglas models and lungs of anesthetized dogs will be compared with a mathematical model, which will be developed using basic principles in aerosol science. The mathematical model should have application in aerosol therapy.